<style>
    div {
        position: relative;
        box-sizing: border-box;
        background-color: blueviolet;
        width: 200px;
        height: 0.5px;
        margin-top: 10px;
        /* box-shadow: 0px 0px 0px 0.5px green; */
    }

    /* div::after {
        position: absolute;
        content: "";
        background-color: red;
        width: 100%;
        height: 0.5px;
        bottom: 0px;
    } */
</style>
</head>

<body>
    <div></div>
</body>